Hydrocephaly is a condition in which the body, for any of several reasons, is unable to relieve itself of excess CSF collected in the ventricles of the brain, resulting in increased epidural and intradural pressures. This in turn causes adverse physiological effects including compression of brain tissue, impairment of blood flow in the brain tissue and impairment of the brain's normal metabolism.
Drainage valves for the treatment of hydrocephaly are known. Such valves control the drainage of excess CSF from the ventricles of the brain to a suitable drainage location elsewhere in the body such as the peritoneal cavity. CSF drainage valves include check valves, servo valves and combinations thereof. Check valves, for example, operate by opening when the fluid pressure differential between the inlet and outlet openings of the valve exceeds a predetermined threshold value. When opened, the valve allows CSF drainage and thereafter prevents the differential fluid pressure from exceeding the threshold value.
The art, however, has generally failed to provide a valve mechanism for CSF valves to compensate for the differences in liquid column height that occur when the patient rises from a recumbent position. In such a situation, the differential fluid pressure normally increases because of a resulting increased vertical height of the fluid column between the patient's head and the selected drainage location elsewhere in the patient's body. Although such an increase in differential pressure is normal, a check valve, for example, will typically respond by opening and thereby allowing undesired hyperdrainage of the ventricular spaces and possibly causing a potentially serious hematoma. Accordingly, it is desirable to provide an implantable pressure relief valve for the treatment of hydrocephaly which is effective in shunting CSF in response to abnormal intracranial pressures while avoiding hyperdrainage in the event of normal variations in fluid pressure.
The present invention is directed to an implantable valve designed to remedy the aforementioned problems and drawbacks of the prior art by providing a valve having a valving mechanism which allows CSF drainage only when the pressure differential between the area of the brain to be drained and the drainage location in the body exceeds a predetermined threshold value.
The valve of the present invention includes a deformable diaphragm housed within a hermetically sealed unit. The unit includes inlet and outlet ports for the passage of CSF therethrough. The diaphragm includes a fluid flow orifice to direct the flow of CSF from the inflow port through the orifice and to the outflow port for drainage. A valving mechanism is positioned within the fluid flow orifice and includes a spherical member or ball seated within a tapered or conical valve seat. The ball is retained within the seat under the force exerted by a compression spring which coacts with the ball to keep the valve in a closed condition when the valve experiences normal variations in CSF pressure.
Variations in the pressure differential across the valve caused by changes in the fluid column height, such as when the patient arises from a lying or recumbent position, are compensated for by the action of the flexible diaphragm. Such normal pressure variations will cause a pressure variation across the valve which deforms the diaphragm slightly while maintaining the ball within the conical seat in the fluid flow orifice. Excessive intracranial pressures, however, will cause the valve to open by exerting additional force directly against the ball and the compression spring. Compression of the spring will unseat the ball and thereby open the valve to allow CSF to flow through the orifice to the outflow port and to a suitable drainage location.
In one embodiment of the invention, the diaphragm divides the valve housing into first and second chambers. The first chamber is associated with the inflow port on the valve and is maintained at ambient pressure while the second or outflow chamber is maintained at a pressure equivalent to the pressure of the drainage location within the body. Flexible tubing connects the fluid flow orifice within the diaphragm to the inflow port in the first chamber to maintain the valve seat and the ball seated therein at intracranial pressures. In this arrangement, the ball remains firmly seated within the valve seat as long as the pressure differential across the valve remains at a substantially constant predetermined value. Differences in fluid column height are compensated for by flexing of the diaphragm while the ball remains firmly seated within its valve seat.
In a second embodiment, the valve is again provided within a hermetically sealed housing having first and second chambers. The first chamber is in fluid communication with the inflow port on the valve. The second chamber is in fluid communication with the outflow port for drainage of excess CSF. The first chamber is maintained at the fluid pressure of the CSF source location while the second chamber is maintained substantially at the fluid pressure of the drainage location. Pressure differentials across the diaphragm will cause both the flexible diaphragm to become deformed and, when the pressure differential exceeds a first predetermined threshold value, the ball member will be unseated to open the fluid flow orifice between the first and second chambers, thereby allowing drainage of CSF.
It is accordingly an object of the present invention to provide a device for the relief of excess cerebrospinal fluid pressure for use in the treatment of hydrocephaly and the like.
It is another object of the present invention to provide a drainage valve suitable for cranial implantation and useful in the treatment of hydrocephaly.
It is another object of the present invention to provide a drainage valve useful in the treatment of hydrocephaly and which prevents excess drainage of CSF in the event of normal increases in differential fluid pressures such as when the patient arises from a recumbent position, for example.
These and other objects of the present invention will be more clearly understood by those skilled in the art following a consideration of the remainder of the disclosure, including the detailed description of the preferred embodiments and the appended claims.